Painful Posteromedial Ankle Mass Caused by Posterior Tibial Nerve Schwannoma: A Case Report

Abstract

Background: Benign peripheral nerve sheath tumors (schwannomas) are uncommon and form from Schwann cells, which are found in nerves. If it exists at this site, it may appear to be a more common cause of ankle pain and often is not suspected outside of the imaging modality.

Case report: We present a 56-year-old Hispanic woman with progressive sharp pain in the left lower extremity (LLE) for two years, who was found to have a palpable posteromedial ankle mass and paresthesia radiating to the calf and dorsum of the foot. MRI showed a high-contrast well-defined, fusiform lesion that extended along the course of the posterior tibial nerve suggesting the possibility of schwannoma. An elective surgical excision of the tibial nerve with external neurolysis of the nerve in the space of the adjacent neurovascular and tendinous structures was performed. The pathological examination showed a benign schwannoma with classic Antoni A and B features, nuclear palisading, and verocay bodies, free of atypia, necrosis or mitosis. Limited resources precluded immunohistochemical staining and diagnosis was based on typical histomorphology alone. Transient paresthesia in early postoperative period were found to be completely resolved and patient showed no complaints at 1-month follow-up, with no neurological deficit noted and normal gait.

Conclusions: Posterior tibial nerve schwannoma should be included in the differential diagnosis for patients with a chronic painful posteromedial ankle mass with a positive tinel sign and radiating paresthesia. The magnetic resonance imaging (MRI) is useful for localizing the neural origin of the lesion preoperatively, with the planning of the nerve-sparing surgical approach, and the complete microsurgical removal with neurolysis provides an excellent functional and oncological results.